The behaviour of selenium in anode during electrolysis was investigated in terms of the impurity level in anode, the concentration of dissolved oxygen and the condition of heat treatment of anode. The spherical and ellipsoidal Cu2Se particles surrounded by films of Cu2Se and Cu2O mixture were found in the anode before electrolysis, regardless of the concentration of selenium and oxygen in the anode. These Cu2Se particle did not dissolve, forming the anode slime during electrolysis.
The passivation was not observed at a current density of less than 2 A/dm2, but occured at a current density of 3 A/dm2. On the way of this passivation, part of the slime is decopperized and changes to compounds of Cu2 -xSe (100 mV), Cu3Se2 (440 mV) and CuSe (740 mV), successively, according to the anode potential.
The heat treatment of anode makes Cu2O particles in the Cu2Se-Cu2O mixture film coarsen and separate from the mixture. The slimes formed on the anode with longer-time heating treatment adhered to it strongly and thus, the passivation was accelerated.
